This invention relates to a cylinder lock of the type in which an elongated plug is rotatably supported in a cylinder. Axially spaced and radially movable driver pins are slidably supported in holes in the cylinder while axially spaced and radially movable tumbler pins are slidably supported in holes in the plug. The tumbler pins in the plug are alined axially with the driver pins in the cylinder and normally are alined angularly with the driver pins. The interface between each tumbler pin and each alined pin in the cylinder normally is spaced radially from a shear line located between the plug and the cylinder. As a result, the pins prevent the plug from being turned in the cylinder and thereby prevent the lock from being operated.
When a proper key is inserted into a keyway in the plug, the pins are shifted radially to cause the interfaces between the tumbler pins and the alined pins in the cylinder to lie precisely on the shear line. The plug then may be turned by the key to effect operation of the lock.
In certain locks, and particularly in door locks for apartments, it is desirable to be able to re-key the lock, that is to say, to change the lock over so that it no longer can be operated by the original user key and can only be operated by another user key with different bitting. When an apartment door lock is rekeyed, a former tenant who has retained a key is prevented from using the key to unlock the door of the new tenant.
A locksmith may re-key a lock by disassembling the lock and replacing one or more of the pins with a pin or pins of different length. In some locks, re-keying may be effected by the building owner or superintendent by inserting a special change key into the plug in order to change the effective length of one or more pins. Examples of such locks are disclosed in U.S. Pat. Nos. 3,078,705; 4,412,437 and 4,440,009. These locks require the use of special spacers which must be removed from the lock to change the effective length of the pins.